Various methods are known for producing images or duplicates of images. The imaging materials used are, in certain cases, particular inorganic compounds and, in other cases, particular organic compounds. Some of these heretofore known methods employ mixtures of inorganic compounds such as silver halide with one or more particular types of organic compounds as sensitizers.
A new photographic process using tellurium compounds to provide the image is disclosed in U.S. Pat. No. 4,142,896. In accordance with U.S. Pat. No. 4,142,896, an emulsion is formed using certain reducible precursor in a binder suitable for forming a film-like coating on a substrate. The film prepared thereform is exposed imagewise to activating energy and may be thereafter developed as is known in the art hereinafter described. Heat development is preferred.
Some tellurium compounds described for use in the photographic process of U.S. Pat. No. 4,142,896 may be represented, for example, by the formula: EQU R.sub.x -Te-X.sub.y
in which R is an organic radical containing at least one carbonyl group, X is halogen, preferably chlorine, and X is 1, 2 or 3, and x+y=4. The organic radical R may be either two independent radicals or may be joined together to form a cyclic compound. Another group of compounds mentioned in U.S. Pat. No. 4,142,896 are organic tellurium compounds which may be considered or characterized as tellurium tetrahalide adducts of ethyleneic or acetyleneic hydrocarbons. Some of such compounds can be represented by the formulae: ##STR4## wherein R and R.sup.1 are each the residue of an ethyleneic hydrocarbon, and X is a halogen, preferably chlorine.
Another broad category of photosensitive tellurium compounds which have been found useful are halogenated tellurium compounds, such as compounds of the formula EQU TeCl.sub.n Br.sub.m
where n is an integer from 2 to 4, and n+m=4. The use of such halogenated tellurium compounds in imaging processes is disclosed in U.S. Pat. No. 4,066,460 to Chang et al.
Still another category of useful tellurium compounds are described in U.S. Pat. No. 4,106,939. These compounds are tellurium tetrahalide adducts of aromatic amines in which the nitrogen attached directly or indirectly to the aromatic ring is substituted by alkyls of 1-4 carbon atoms, the adduct being free of diazo groups.
The tellurium compounds such as the foregoing may be employed in conjunction with a reductant precursor which serves as a sensitizer. The reductant precursor is a compound which, under the influence of activating energy, will absorb radiation energy and abstract labile hydrogen from an appropriate hydrogen donor to become a strong reducing agent. The strong reducing agent reduces the tellurium compound, which results in a change in optical density suitable for recording information. In general terms, the foregoing reaction may be represented by the following mechanism: ##STR5## wherein PQ is the reductant precursor sensitizing agent; .sup.1 PQ is the first excited singlet state thereof; .sup.3 PQ is the triplet state thereof; RH is the hydrogen donor; PQ.H.sub.2 is the reductant precursor in its reduced state; and (R.sub.1).sub.2.Te.X.sub.2 is the reducible tellurium image-forming compound.
In this connection, it should be noted that the hydrogen donor need not be specifically provided, although a variety of alcohols can be used if desired. In the absence of a specially provided hydrogen donor, the labile hydrogen can sometimes be abstracted from the organic resins used as binders. In other cases, the sensitizer can be its own hydrogen donor, and this is known to be the case with at least one preferred sensitizer, namely, isoproxynaphthoquinone.
A modification of the tellurium photographic process is described in Belgian Patent No. 854,193, where certain diols of the formula EQU R.sub.10 --CHOH--Z--CHOH--R.sub.11
may be employed as the hydrogen donor for use in conjunction with the photosensitizer described above. In the foregoing formula, R.sub.10 and R.sub.11 represent hydrogen and various organic substituents. Z may be a direct carbon-carbon linkage between the two hydroxy-substituted carbon atoms, or may be any of various linking groups. Reference is made to Belgian Patent No. 854,193 for a fuller description of the diols referred to. In the Belgian patent, these diols are said to serve as hydrogen donors. Subsequent research has suggested that this is not completely accurate. In fact, a major portion of the diol appears to form a complex with the tellurium compound.
This finding has led to the discovery of diols of the general formula EQU R--O--CH.sub.2 CHOH--CH.sub.2 OH
which has improved characterisitcs when used in tellurium-based photographic films.
The radical R may be a simple aliphatic group (for example, alkyl or alkenyl). Alternatively, the radical R may contain a carbonyl group (for example, an acyl radical). Preferably, however, the radical R is aromatic. Best results are obtained where the aromatic ring is separated from the ether oxygen by one methylene grouping. A more complete description of these diols is contained in co-pending application Ser. No. 073,700 filed Sept. 10, 1980.
Still another modification in the use of tellurium compounds as photosensitive agents involves what is known as a "masked reducing agent." A number of compounds are known, such as phenidone, which will reduce organo-tellurium compounds. The reducing capacity of such compounds may be "masked"--i.e., inhibited--by appropriate substitution. In such cases, if the substituent is one which can be cleaved by the reaction products liberated upon the photoreduction of the tellurium compound, the masked-reducing agent can be used to amplify the photo-response through the mechanism: ##STR6##
Since the tellurium compounds commonly used release hydrogen halides (particularly hydrogen chloride) as by-products of the reduction reaction, and the reducing agents, such as phenidone, are amino compounds, the masking agents most effectively employed are compounds which will convert the amino nitrogen into an amide. A typical masked reducing agent thus is the compound: ##STR7## A more complete description of the masked reducing agent may be found in Belgian Patent No. 863,052, and reference thereto is made for an additional description thereof.
In practice, the foregoing ingredients, i.e., a tellurium derivative, a reductant precursor, and the optional ingredients such as the glycol and a masked reducing agent, are combined in a suitable matrix to form an emulsion which is supported by an appropriate carrier. A latent image is formed by exposure to an appropriate imaging energy (for example, a light image). The latent image is thereafter developed by heating the exposed film as described in U.S. Pat. No. 4,142,896.
Alternately, the latent image may be induced by using an electron beam or an electric current as the activating energy. Since electrons so introduced into the film are capable of acting directly on the tellurium compound when such activating energy is used, the reductant precursor can be omitted from the composition.
Other forms of activating energy will be recognized by those skilled in the art, and can also be applied under appropriate conditions.